In modern power generation plants and other manufacturing industries requiring large volumes of water, it is a well recognized problem that there is a potential loss of water from the adherence to and buildup of a variety of foreign substances on the exposed surfaces of fluid transport systems. Such surfaces of the fluid transport systems include, but are not necessary limited to, the inner surfaces of the water intake pipes, valves, fittings, heat exchangers, etc, and the outer surfaces of screens (rotary & bar), etc. Power generating plants and other manufacturing facilities which require the use of a particular fluid medium, such as fresh water, have long sought an effective method of keeping the fluid transport system operational and free of any buildup of foreign organisms or debris.
One such foreign organism of particular concern and discovered recently is the Zebra Mollusks. Such Zebra Mollusks are better known in the art as Zebra Mussels. See, for example, an article published in the Dec. 1990 issue of "Electrical World" on pages 72-74 and another article published in the Jul. 1990 issue of "The Atlantic Monthly" on pages 81-87. The disclosures of these particular articles are incorporated herein by referenced thereto.
Prior to the present invention, when the fluid transport systems of current technology exhibit diminished capacity due to clogging by foreign substance buildup, one method of servicing a submerged piping system would be to have a person use a dragging device to pull through the fluid transport system to dislodge the buildups or clogs and subsequently pull them through to the exit for manual cleanup. Drawbacks to this prior art method are readily apparent and would include the fact that this method is not only labor-intensive but also time-consuming. Also this method cannot be accomplished continuously, but must be done on a regularly scheduled basis.
Another possible cleaning method used for facilities, such as water treatment plants, includes flushing the fluid transport system with relatively large quantities of chemicals such as chlorine or potassium chloride. While this process can be conducted in a continuous manner, it is not efficient or cost-effective to induce large quantities of chemicals into the desired fluid medium which in some cases may be detrimental and must later be separated out.
As discussed in the above-referenced articles, three types of problems have been identified with Zebra-Mussel fouling in water intake systems. Initially, layers of attached mussels will reduce or block flow, even through large-diameter piping, trash racks, and traveling screens. Eventually, shells or clumps of shells breaking free of their attachment sites can block openings in piping, heat exchangers, strainers, or traveling screens. Finally, attachment points accumulate other debris and serve as sites for corrosion.
There are three EPA-approved chemical methods that have been tried in US powerplants-chlorination, the most discussed method; bromination, primarily Acti-brom, a Nalco Chemical Co (Naperville, Ill.) product; and Betz Laboratories' (Trevose, Pa.) Clam-trol. Several other chemical treatments have been tried in laboratory tests, but not in a utility or industrial environment. Chlorination is the most common chemical control for Zebra-Mussel fouling. Continuous chlorination at 0.3 ppm for up to three weeks is required to achieve efficacy. Intermittent chlorination programs, that feed a few hours daily have been found to be ineffective. Using other chemicals-such as ozone, hydrogen peroxide, and potassium permanganate is possible, but expensive, environmentally unsound, and/or impractical to distribute throughout a cooling system. It has been reported that Detroit Edison is trying to control mussels by scraping and hydroblasting during regular maintenance. Janiece Romstadt has received federal permission to use a commercial mollucicide. Ontario Hydro is treating some of its coolant with hypochlorite, an oxidant that chews away at the soft parts of the organism and is the active ingredient in household bleach; the utility admits, however, that this short-term solution is offensive to a public anxious about the environment. One alternative is ozonation. Like hypochlorite, ozone is an oxidant; it is also environmentally benign. But it is extremely expensive. Ontario Hydro estimates that ozonation would cost it $9 million per plant.
One member, of the U.S. Fish and Wildlife Service, puts the bill for re-engineering, maintenance, and other forms of mussel abatement at almost half a billion dollars a year. But none of the emergency measures, though they may alleviate specific problems here and there, will do anything to halt the overall proliferation of Zebra Mussels. The mussels are very strongly byssate and they will attach to insides and occlude the openings of industrial and domestic pipelines, clog underground irrigation systems of farms, greenhouses, and any other facility that draws water directly from the Great Lakes, encrust navigation buoys to the point of submerging them, and encrust, hulls of boats and other types of sailing craft that remain in the water over the summer and fall. The mussels may also become a significant vector of parasites that are lethal to game species of waterfowl and fish.
In the November 1991 issue of "Underwater USA" a news article appeared which indicated that, the tiny but dreaded Zebra Mussel has been discovered for the first time in a section of the Mississippi River near La Crosse, Wis., a U.S. Fish and Wildlife Service toxicologist reports.
One expert says that he expects to see the Zebra Mussel population explode by next year. Worse, it's likely boaters will inadvertently introduce the Zebra Mussels to Minnesota lakes.
The mussels have an extremely hard shell and clog water intakes at power plants and municipal water systems.
The Monroe, Mich., water supply was crippled for three days when the mussels clogged all intake pipe. Water bills increased 18 percent to pay for removing them.
An Ontario electric company spent $10 million on chlorine to keep the mussels out of power plant water intake pipes.
This expert expects the same things to happen at power and water plants on the Mississippi. He says locks and dams also are favored by the mussels, which cause leaks and prevent gates from closing completely.
Another material being marketed to control marine fouling of boat hulls was developed by a chemical company in the eighties. Use of this material, however, is difficult. It requires a considerable amount of preparation of the substrate. According to the manufacturer's instruction sheet, for example, all previous bottom paint must be removed down to a gelcoat. If an epoxy barrier coat has been previously applied, the barrier coat must be profiled with a sand-blaster or wet blaster using 40 F grit or ground using 60-80 grit paper. The waterline should be preserved using duct or similar tape. The top sides should be masked to protect against etching and overspray. The blasted surface should be vacuumed and wiped thoroughly. The hull is then inspected for blisters and defects. Any defects discovered are repaired using conventional repair techniques. Any repair required is done using any standard 2 part epoxy base repair material. A polyester resin base repair material cannot be used.
Fairing of the repaired areas is then done. Any unfaired areas will be very apparent in the finished hull and will make activation of the material difficult. Grit and dust are then removed with an acetone tack cloth. The moisture in the hull, as determined by a Sovereign model 452B or similar moisture meter, must have a reading below 12 and the reading should be reduced to as close to 5 as practical. Because this material is an excellent moisture barrier any moisture Left in the substrate will be trapped and react with unreacted solvents in the polyester substrate resulting in blister formation.
The next step is an application of primer. This primer is a very low viscosity, 100% epoxy undercoat. Like wood preservative it has very high "wicking" characteristics. Only one light coat is required. It may be sprayed without thinning. A quart will cover approximately 400 square feet (approximately the wetted surface of a 42 foot full keel sailboat.) This is a tack coat and should be applied similar to a wax as opposed to a paint application. A thick coat will cause a top coat of the material to run and bleed. The primer will cure to a "tacky" surface in 3 to 4 hours. It is only to be used as an undercoat and will oxidize if not covered with a finish coat The finish coat may be applied any time after the surface becomes "tacky" to touch, but within the 8 hour window.
Preparation of the coating material is now ready. This material is subject to settling; seven different ingredients are used to obtain its unique qualities of strength, flexibility, electrical-resistance, and anti-fouling properties. To assure uniformity Part A of the material must be thoroughly mixed to a uniform "cake icing" consistency before adding Part B, the hardener. Mixing should be done using an electric drill and a paint mixing agitator. It is good practice to mix Part A each time prior to removing sub-lots from the primary container. Care must be taken when mixing the material in the plastic container. The agitator should have no protruding edges that might cut the plastic. Plastic slivers may get in the mix and ultimately clog the spray nozzle. In addition, the hardener must be thoroughly mixed before adding to Part A. Three parts by volume of Part A, the epoxy base, is mixed with 1 part by volume of Part B, the activator. At 70 degrees F the mixture has the consistency of dry wall joint compound. Heated to 110 degrees F the consistency is that of latex paint. The pot life at 70 degrees F is about 1 hour, and at 105 degrees F is about 20 minutes.
The material is now ready for application. One serious drawback of this material is that careful attention must be paid to the material's application window; the material should be applied while the primer is still "tacky". If the application window is missed, the surface should be re-profiled with 60-80 grit sandpaper, cleaned, and lightly covered again with the primer before proceeding. The material is applied using a standard cup gun commonly used in automobile painting. Add Part A and Part B to the cup in the proper proportion and blend. Add 15-20% solvent to the cup and close immediately.
Mix the components by shaking and swirling the gun. Spray using 60-80 psi air pressure.
A 0.001-0.002 inch thick tack coat is first sprayed over the primer and then followed in 10-45 minutes by a 0.004-0.005 inch thick coat. Following with a full 0.003-0,005 inch coat until a finish thickness of 0.017-0.020 inch is obtained. Re-coats may be applied every 10-15 minutes at 70 degrees F. Runs may occur if coats are too thick, subjected to very warm environments, or exposed to direct sunlight. Another disadvantage of this material is that operator judgement is critical when application is done at less than ideal conditions.
If the cup gun does not have an agitator, the gun must be frequently shaken with a rapid wrist motion to keep a uniform mixture. A pressure pot may be used for larger jobs. A Bink's model 7 gun, a 2 gallon Bink's pot with agitator, model #83-5508, air regulator model #85-204 and a 38 PM nozzle combination has been used successfully. The 38 PM nozzle is quite large (about 0.086") and the applicator may prefer a nozzle in the 0.060 range to obtain greater control of film thickness.
The material is allowed to cure for twenty-four to forty-eight (24 to 48) hours, depending on ambient conditions, before activating. This activation step is very important, because barnacles will grow on unactivated material. Lightly sandblasting, either wet or dry, with 40 F grit or finer will activate the surface or lightly sand with 220 wet/dry paper to remove blush. The longer the cure time before activating the easier it is to activate successfully. The material will continue to cure for a week at 70 degrees F.
The boat may be put in the water anytime after activating. Although the material is formulated for highly moist environments and will cure under water, it should not be applied to damp surfaces.
Therefore, it is apparent that it is desirable to create a fluid transport system in which the pipes and other system components are manufactured, or lined, or coated with a material which would substantially minimize the initial adherence to and eventual buildup of foreign substances on the inner surfaces of the pipes and the exposed surfaces of other system components while they are submerged in a fluid medium. It is also apparent that it is desirable to develop a material which can be coated on buoys and boats to prevent attachment of the Zebra Mussel or other marine organisms thereto.